The subject matter disclosed herein relates to a mechanism for a circuit breaker. In particular, the subject matter disclosed herein relates to a mechanism coupled to a contact arm to provide current limiting functionality by reducing the opening time.
Air circuit breakers are commonly used in electrical distribution systems. A typical air circuit breaker comprises an assembly of components for connecting an electrical power source to a consumer of electrical power called a load. The components are referred to as a main contact assembly. In this assembly, a main contact is typically either opened, interrupting a path for power to travel from the source to the load, or closed, providing a path for power to travel from the source to the load. In a particular type of circuit breaker, referred to as an air circuit breaker, the force necessary to open or close the main contact assembly is provided by an arrangement of compression springs. When the compression springs discharge, they exert a force that provides the energy needed to open or close the main contacts. Compression springs that provide a force to close the main contacts are often called closing springs. Compression springs that provide a force to open the main contacts are often referred to as contact springs.
The mechanism for controlling the compression springs comprises a configuration of mechanical linkages between a latching shaft and an actuation device. The actuation device may be manually or electrically operated. An electrically operated actuation device generally operates when a particular electrical condition is sensed, for example, over-current or short-circuit conditions. The actuation device within the circuit breaker typically imparts a force onto a linkage assembly. The linkage assembly then translates the force from the actuation device into a rotational force exerted on the latching shaft. The latching shaft then rotates. This rotation is translated through the mechanical linkages to unlatch or activate either the closing springs or the contact springs. There is typically a first latching shaft mechanically linked to the closing springs called the closing shaft. A second latching shaft is mechanically linked to the contact springs called the tripping shaft.
As each actuation device acts upon the latching shaft via a corresponding linkage assembly, the linkage assembly acts as a lever converting a linear force from the actuation device to a rotational force on the latching shaft. The time required for the actuation device to be electrically activated and initiate movement of the mechanism and the contact assembly can be lengthy. Where an undesirable electrical condition exists, this time period required to open the contact assembly may be longer than desired.
While existing circuit breakers are suitable for their intended purposes, there still remains a need for improvements particularly regarding the operation of the circuit breaker and the time required to open the contacts under high current and short circuit conditions.